I'm skeptical of Musk's claim that Teslas are an "appreciating asset". That doesn't make sense in the automotive world, and it's claims like this that make him lose credibility.
1. Discontinued / Very few produced -> Tesla is ramping up production 2. Iconic design -> Teslas do not have stand out look and the same design language is being used for other Tesla vehicles too. 3. Movie / cult classic -> Tesla does not have its 'Back to the Future' or 'Fast and the Furious'. 4. Unique features not present in other cars-> Tesla doesn't necessarily have any
Lastly, tablet and screen based designs are ones that age the worst. So, Tesla is at a disadvantage there.
The car collector's market is completely at odds with what Tesla offers. Tesla lovers are high technology folk, who always want the latest and the greatest. They do not appreciate dated designs. Car collectors are the ones most averse to electric cars (as of now).
I think Teslas will hold their price better than other brands, but they certainly won't appreciate. (may be the original roadster, because they made so few of them)
I don't know if his statement was about the financial depreciation of a Tesla or not, but if in 6 months, my car is better than it is today, with no custom parts or additions, you can undoubtedly claim that its value (the perception of what the car is doing for me) increased. Though, not its financial value.
Of course the use of the term 'asset', since it is typically used for financial value, is confusing if that was his intended meaning.
Well, there are plenty of cars which are appreciating from the moment you pick them up from the dealership. Rare limited editions of Lamborghinis, Ferraris and Porsches all come to mind. But those are rare exceptions from the rule, and Teslas are nowhere near that status.